linux-kernel - [PATCH 1/5] sysctl: Clarify how the ctl

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Date:   Wed,  7 Mar 2018 15:34:25 -0500
From:   Waiman Long <longman@...hat.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH 1/5] sysctl: Clarify how the ctl_table.flags should be set

Additional comments are added to clarify how the ctl_table.flags
field should be set as well as precaution on what needs to be done
when additional flags are defined in the future.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 include/linux/sysctl.h | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 3db57af..bc09361 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -125,7 +125,7 @@ struct ctl_table
 } __randomize_layout;
 
 /**
- * enum ctl_table_flags - flags for the ctl table
+ * enum ctl_table_flags - flags for the ctl table (struct ctl_table.flags)
  *
  * @CTL_FLAGS_CLAMP_RANGE: Set to indicate that the entry should be
  *	flexibly clamped to min/max range in case the user provided
@@ -134,10 +134,23 @@ struct ctl_table
  * 	had been issued for that entry.
  *
  * At most 16 different flags will be allowed.
+ *
+ * The flags can be set in two different ways. They can either be
+ * statically set at definition time or dynamically set at run time.
+ *
+ * Currently, only the CTL_FLAGS_OOR_WARNED flag is set at run time.
+ * No locking or atomic access to set @CTL_FLAGS_OOR_WARNED is needed
+ * in the current use case. If similar dynamic flags are defined in the
+ * future, we may need to revisit again to see if atomic access or
+ * locking is needed to prevent lost changes due to concurrent updates
+ * to the flags field.
  */
 enum ctl_table_flags {
+	/* Statically set flags */
 	CTL_FLAGS_CLAMP_RANGE		= BIT(0),
-	CTL_FLAGS_OOR_WARNED		= BIT(1),
+
+	/* Flags set at run time */
+	CTL_FLAGS_OOR_WARNED		= BIT(8),
 };
 
 struct ctl_node {
-- 
1.8.3.1